1. Field of Invention
The invention relates to an auto gain controller, and more particularly to an auto gain controller without the need of a DC offset canceling circuit.
2. Description of Related Arts
In order to find out the signal strength that needs to be adjusted, the traditional digital auto gain control circuit uses a set of collected signals to calculate the present dB value and subtracts the targeted dB value. Then, the signal is passed to an amplifier to amplify its signal strength to the targeted signal strength.
As shown in FIG. 1, an analog signal is passed to the amplifier 101 for amplification and to an analog-to-digital converter (not shown) for conversion. Then, the converted digital signal is passed to a DC offset cancellation circuit 102 for canceling its DC offset. Then, the output signal from circuit 102 is passed to a calculation circuit 103 for calculating the strength or energy of the present signal. Then, the calculated signal is passed to another calculating circuit 104 for calculating the signal value that need to be adjusted.
However, if the calculation is processed by the time that DC offset cancellation circuit hasn't finished its job, the error would arise due to the amount of DC offset and the present signal are calculated together. In order to make the digital auto gain control circuit adjust to the corrected targeted signal strength, the digital auto gain control circuit has to wait until the DC offset is cancelled and the current signal is calculated correctly. As a result, the auto gain control circuit would spend more time to achieve the result.
In addition, some auto gain control circuits start working after the cancellation of the DC offset is canceled by using electrical noise. However, the DC offset sometimes is varying along with the changing of the temperature or the gain value. Therefore, the noncancelable DC offset sometimes still exists after the beginning of the auto gain control. Consequently, the auto gain control cannot adjust to the targeted value because of the error of calculation.